The use of citrullinated peptides for the diagnosis and prognosis of rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes joint inflammation and extra-articular manifestations. To prevent progressive and irreversible structural damage, early diagnosis of RA is of paramount importance. Antibodies directed against citrullinated proteins and peptides (ACPAs) are the most specific serological markers available for diagnosing RA. ACPAs may be detected several years before symptoms appear, and their presence at disease onset is a good predictor of the development of erosive joint lesions. Synthetic peptides can replace cognate proteins in solid-phase assays for specific autoantibody recognition in RA patients. The use of synthetic peptides instead of proteins represents an advantage in terms of the reproducibility of such immunoassays. They give absolute control over the exact epitopes presented. Furthermore, it is difficult to prepare sufficient amounts of high-quality antigenic proteins with a well-defined degree of citrullination. Synthetic citrullinated peptides, in contrast, are easily obtained in a pure form with a well-defined chemical structure and the epitopes can be precisely oriented in the plate by covalent binding of the peptides. We have recently obtained and highlighted the application of chimeric peptides bearing different citrullinated protein domains for the design of RA diagnosis systems. Our results indicate that more than one serological test is required to classify RA patients based on the presence or absence of ACPAs. Each of the target molecules reported (fibrin, vimentin and filaggrin) helps to identify a particular subset of RA patients.